With renewal and replacement of network products, a size and power consumption of a module used in a network are continuously decreasing, so as to meet requirements for continuous cost reduction and continuous performance improvement. Featuring a subminiature size, a low cost, and the like, silicon-based photonic devices have attracted wide attention from the industry in recent years, and become one of key directions that are considered in renewal and replacement of network products.
In the prior art, a process error of a silicon waveguide has a relatively high impact on a refractive index of the waveguide. The impact causes random changes in refractive indexes of different parts of the silicon waveguide. Consequently, there is a relatively significant random change in an operating wavelength of a silicon-based photonic device, or performance of crosstalk between paths of the device deteriorates. In addition, a relatively large refractive index difference further causes quite high polarization dependence of the silicon waveguide, which is unfavorable for implementing polarization-insensitive work. Further, the silicon waveguide is highly sensitive to temperature, and can work properly only within a proper temperature range.
A silicon-based arrayed waveguide grating is a quite important silicon-based photonic device. Because the silicon-based arrayed waveguide grating can implement wavelength splitting for a large quantity of wavelengths at the same time and control multiple wavelengths in a unified manner, and has a wide free spectral range and a compact device size, the silicon-based arrayed waveguide grating is considered as an important alternative to upgrading an optical splitter in network products.
However, the silicon-based arrayed waveguide grating is still restricted in terms of materials, and performance of an optical splitter to which the silicon-based arrayed waveguide grating is applied still cannot meet a requirement, which are mainly reflected as follows: Firstly, the silicon-based arrayed waveguide grating is highly sensitive to a process error, and has a crosstalk value of less than 15 dB, which cannot meet application requirements of some networks. For example, a crosstalk value of at least 25 dB is required in a passive optical network (Passive Optical Network, PON) for short, and a crosstalk value of at least 35 dB is required in a 40G-PON with two stages of optical splitters. Secondly, the silicon-based arrayed waveguide grating is highly sensitive to temperature, and there is no mature a thermal solution; therefore, a semiconductor thermoelectric cooler (TEC for short) is required to perform temperature control, which also increases power consumption. Thirdly, because a refractive index difference of a silicon waveguide is large, polarization dependence is quite high. Because of the quite high polarization dependence, the silicon-based arrayed waveguide grating can hardly implement polarization-insensitive work required by optical splitting; instead, a polarization diversity manner needs to be used, that is, two devices are used to respectively process two beams of polarized light. However, in the polarization diversity manner, a device volume definitely increases, which is unfavorable for device miniaturization. In view of the foregoing undesirable factors, performance of the silicon-based arrayed waveguide grating urgently needs to be improved.
According to a result of a theoretical research, crosstalk of an arrayed waveguide grating is mainly subject to a random phase error of an arrayed waveguide that is caused by a process error. Causes for generation of this random phase error are mainly classified into two types: One type is non-uniformity of a material of an arrayed waveguide, and the other type is a random change in a refractive index of an arrayed waveguide. Generally, a random change in a refractive index of an arrayed waveguide is a leading factor that causes a random phase error. Therefore, researchers mainly optimize crosstalk performance of an arrayed waveguide grating by changing a structure of an arrayed waveguide. Currently, two methods may be used to increase a crosstalk value of a silicon-based arrayed waveguide grating: increasing a width of an arrayed waveguide, and using a ridge waveguide with a relatively small refractive index difference as an arrayed waveguide. However, even if these optimization methods are used, the crosstalk value of the arrayed waveguide grating still cannot meet a system requirement. Specific comparative embodiments are as follows: